This invention relates in general to valves for controlling fluid flow and more particularly, to a fluid flow control assembly for controlling fluid flow in two directions of flow through a pilot-operated main spool valve, and having a check valve arrangement forming a fluid rectifier circuit to provide unidirectional fluid flow through a pilot valve operating the main spool valve.
Valves are widely used for controlling the flow of a fluid from a source of pressurized fluid to a load device or from a load device to a low-pressure reservoir. Frequently, a pump, or other device, is provided as the source of pressured fluid. The flow of the fluid is selectively controlled by a valve to control the operation of the load device.
One type of valve is a microvalve. A microvalve system is a MicroElectroMechanical System (MEMS) relating in general to semiconductor electromechanical devices.
MEMS are a class of systems that are physically small, having some features or clearances with sizes in the micrometer range or smaller (i.e., smaller than about 10 microns). These systems have both electrical and mechanical components. The term “micro machining” is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS fabricators originally used modified integrated circuit (e.g., computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micro machine these very small mechanical devices. Today there are many more micro machining techniques and materials available. The term “MEMS device” as may be used in this application means a device that includes a micro machined component having some features or clearances with sizes in the micrometer range, or smaller (i.e., smaller than about 10 microns). It should be noted that if components other than the micro machined component are included in the MEMS device, these other components may be micro machined components or standard sized (i.e., larger) components. Similarly, the term “microvalve” as may be used in this application means a valve having features or clearances with sizes in the micrometer range, or smaller (i.e., smaller than about 10 microns) and thus by definition is at least partially formed by micro machining. The term “microvalve device” as may be used herein means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micro machined components or standard sized (i.e., larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the valve blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
One specific type of microvalve system is the pilot-operated microvalve. Typically, such a microvalve device includes a micro spool valve that is pilot operated by a microvalve of the type as described above. For example, U.S. Pat. Nos. 6,494,804; 6,540,203; 6,637,722; 6,694,998; 6,755,761; 6,845,962; and 6,994,115, the disclosures of which are herein incorporated by reference, disclose pilot-operated microvalves and microvalves acting as pilot valves.
Microvalve devices have application in many fields for controlling the flow of fluids in systems such as hydraulic, pneumatic, and refrigerant systems, including the Heating, Ventilation, and Air Conditioning (HVAC) field. HVAC systems may include, without limitation, such systems as refrigeration systems, air conditioning systems, air handling systems, chilled water systems, etc. Many HVAC systems, including air conditioning and refrigeration systems operate by circulating a refrigerant fluid between a first heat exchanger (an evaporator), where the refrigerant fluid gains heat energy, and a second heat exchanger (a condenser), where heat energy in the refrigerant fluid is rejected from the HVAC system. One type of HVAC system is the heat pump system, which provides the ability to reverse flow of refrigerant through portions of the HVAC system. This allows the heat pump system to act as an air conditioning system in the summer, cooling air that flows through a first heat exchanger by absorbing the heat from the air into a refrigerant pumped through the first heat exchanger. The refrigerant then flows to a second heat exchanger, where the heat gained by the refrigerant in the first heat exchanger is rejected. However, during the winter, the flow of refrigerant between the first and second heat exchangers is reversed. Heat is absorbed into the refrigerant in the second heat exchanger, and the refrigerant flows to the first heat exchanger, where the heat is rejected from the refrigerant into the air flowing through the first heat exchanger, warming the air passing through the first heat exchanger.